The present invention relates to studio lighting devices, i.e. devices for illuminating subjects for purposes of color photography or cinematography, or for other situations in which it is desirable to illuminate a subject with light having a selected color temperature.
In fields such as color photography and cinematography, the colors appearing in the final product, be it a photographic print or motion picture diapositive, will depend substantially on both the color temperature and the intensity of the light which illuminated the subject during filming.
One of the capabilities required of such a lighting device is that the intensity of the light which it emits be adjustable. Those familiar with electrically powered light sources are aware that, in the absence of special considerations, the most suitable manner of varying the light intensity produced by such a source is by varying the voltage of the operating power supply to the source. However, one characteristic of the light sources currently employed for these purposes is that the color temperature of the light which they produce varies as a function of this voltage. In particular, as the voltage decreases, the color temperature of the light output decreases. Therefore, although this simple technique can be used for monochrome photography and cinematography, it has not proven suitable for filming in color.
Thus, in view of the need to maintain the illumination at a given color temperature, the current practice in the art to employ a variety of techniques, includes the physical placement of light absorbing materials in front of the lighting devices, in order to vary intensity without varying color temperature. All of the techniques currently in use can be implemented only with difficulty, particularly with regard to lighting devices which are installed at a substantial distance above the floor.
It is also possible to vary the intensity of light from such a device by varying the cross-sectional area of the light beam. Specifically, if the width of the beam emitted by the device can be varied from that which is associated with a spotlight to that which is associated with a floodlight, without varying the total light being produced by the device, the intensity of the light reaching the subject will be decreased without altering the color temperature of the beam. However, this technique will permit only a limited adjustment and is not suitable in certain situations where it is desirable to not vary the width of the beam.